Volatilization of Selenium by Alternaria alternata

Abstract

Hills evaporation pond facilities contained between 0.005 and 5 mg of Se per liter. The objective of this study was to isolate Se-methylating organisms in evaporation pond water and to assess, through enrichment and manipulation of their optimal growth parameters, the environmental factors which govern microbial Se methylation. Alternaria alternata was isolated as an active Se-methylating organism. The volatile product was identified as dimethylselenide. The effects of pH, temperature, Se substrates, and methyl donors on the ability of A. alternata to methylate Se were investigated in liquid medium containing 100 mg of Se per liter. The optimum pH and temperature for methylation were 6.5 and 30°C, respectively. Selenate and selenite were methylated more rapidly than selenium sulfide and various organic Se compounds (6-selenoguanosine, 6-selenoinosine, seleno-DL-methionine, and 6-selenopurine). L-Methionine and methyl cobalamine (0.1 ,uM) stimulated dimethylselenide production. This study demonstrates that Se-methylating organisms are present in evaporation pond water and are capable of liberating substantial quantities of Se in the volatile dimethylselenide form. By determining the optimum environmental conditions which stimulate volatilization, it may be possible to design a way to remove Se from seleniferous water in situ. * Corresponding author. first time that A. alternata has been reported to be Se resistant as well as an active methylator of Se. MATERIALS AND METHODS Reagents. Sodium selenite and sodium selenate (Na2SeO4) were obtained from Alfa Products (Danvers, Mass.), and DMSe was from Strem Chemical Co. (Newburyport, Mass.). The following chemicals were obtained from Sigma Chemical Co. (St. Louis, Mo.): selenium sulfide, 6-selenoguanosine, 6-selenoinosine, seleno-DL-methionine, 6-selenopurine, methyl cobalamine, and L-methionine. Sodium tetrahydroborate was obtained from Aldrich Chemical Co. (Milwaukee, Wis.), and ammonium persulfate was from Mallinckrodt (Paris, Ky.). Water sampling. Water samples were collected from evaporation ponds 1, 2, 5, 6, and 7 at Kesterson Reservoir (Merced County, Calif.); from Lost Hills (Kern County, Calif.) A, B, and C evaporation ponds; and from cells 1 to 6 at the Peck Ranch (Fresno County, Calif.) (Fig. 1). The water was collected in Nalgene bottles, transported on blue ice, and stored at 5°C. Atomic absorption spectrometry. Water samples were analyzed for Se atomic absorption spectrometry with hydride generation. The instrument used was a Varian (Mulgrave, Victoria, Australia) Spectra AA/10 with a VGA-76 vapor generation assembly. The operational conditions were as follows: acetylene, 2.4 ml/min; air, 6.3 ml/min; nitrogen, 90 ml/min; sample flow, 6.5 ml/min; acid flow, concentrated

Bioremediation of selenium‐contaminated sediments and water

“…Of the amino acids tested, L-methionine (0.02 g C L −1 ) was found to be the most effective stimulant of DMSe evolution from pond water [47]. The proteins, egg albumen, casein, and gluten (2 g C L −1 ) substantially increased Se biomethylation causing a 23, 41, and 10% Se loss from the inventory, respectively, after 43 d of incubation [47]. It was also observed that Se biomethylation is protein-peptide-limited rather than nitrogen-, amino acid-or carbon-limited [48].…”

“…Increasing the temperature to 35 • C and the addition of 1% (wt/wt) glucose with a fungal inoculum, Alternaria alternata, doubled DMSe production over the controls after 25 d of incubation. Of the amino acids tested, L-methionine (0.02 g C L −1 ) was found to be the most effective stimulant of DMSe evolution from pond water [47]. The proteins, egg albumen, casein, and gluten (2 g C L −1 ) substantially increased Se biomethylation causing a 23, 41, and 10% Se loss from the inventory, respectively, after 43 d of incubation [47].…”

“…Selenium in agricultural drainage water has directly been linked to the death and deformity of waterfowl at California's Kesterson Reservoir [40]. Several studies have been conducted by Frankenberger and his coworkers to determine the optimal conditions to clean up Se-contamination through microbial methylation [14,43,[46][47][48][49]. Thompson-Eagle and Frankenberger [46] isolated Alternaria alternata, an active Se-methylating organism.…”

“…Selenate and selenite were methylated more rapidly than selenium sulfide and various organic Se compounds. In another study, Thompson-Eagle and Frankenberger [47] monitored Se biomethylation from evaporation pond water. Pond water samples (14-2000 µg Se L −1 ) were set up as laboratory mesocosms.…”

REDUCTION OF SELENIUM OXYANIONS BY ENTEROBACTER CLOACAE STRAIN SLD1a-1: REDUCTION OF SELENATE TO SELENITE

“…The instrument used was a Varian (Mulgrave, Victoria, Australia) SpectrAA-10 used in conjunction with a Varian vapor generation accessory (VGA-76). Operating conditions are described elsewhere [11]. This instrument has a limit of detection (LOD) of 0.06 M. With hydride generation, samples must be prepared for analysis in 6 N HCl.…”